The present invention relates to a new and improved construction of infrared intrusion detector which is of the type containing optical focusing means and a sensor arrangement, wherein the infrared radiation received from a number of separate receiving regions is taken-up and evaluated for the purpose of sounding an alarm signal upon there occurring a predetermined change in the received or taken-up radiation.
With such intrusion detectors the infrared radiation which is emitted by an individual at a monitored region is evaluated. If the monitored region is divided into a number of separate receiving regions or fields of view between which there are located dark fields or zones, then each movement of a person causes a modulation of the infrared radiation received by the sensor element. This modulation can be evaluated by means of a conventional evaluation circuit for the purpose of indicating that an intruder has entered the monitored region or area and for the further purpose of giving an alarm signal.
In order to obtain the requisite separate receiving regions or fields of views it is already known in this technology to employ different optical arrangements. A particularly good sensitivity can be realized if there is received from all of the receiving regions as large a quantity of radiation as possible and such received quantity of radiation evaluated. From U.S. Pat. Nos. 3,760,399, 3,829,693 or 3,958,118 there has been taught employing with intrusion detectors for this purpose a reflector which is common to all of the receiving regions or fields of view. This reflector focuses the radiation which arrives from such receiving regions upon a number of juxtapositioned sensor elements. Since there are employed a multiplicity of such sensor elements there is required, however, a complicated and disturbance-prone evaluation circuit at which there is connected the afore-mentioned multiplicity or plurality of sensor elements. Additionally, there is markedly limited the number of possible sensor elements, and thus, the number and selection of the receiving regions.
In other prior art references, for instance, U.S. Pat. Nos. 3,703,718, 4,058,726 or 4,081,680 it is known to avoid these drawbacks in that there is provided a multiplicity of reflectors which, in each case, focus radiation from one receiving region or field of view upon a common sensor element. However, with this system design there must be tolerated the drawback that only a small quantity of radiation is received from each receiving region, and thus, the sensitivity is reduced or the number of receiving regions must be limited.
In German Pat. No. 2,719,191 there is disclosed an infrared radiation intrusion detector wherein the reflector surfaces are constructed as part of a spherical surface, and the selected surface part determines the detectable solid angle. The infrared radiation is conducted to a radiation receiver by means of a radiation conductor bundle composed of a multiplicity of individual radiation-conducting elements, for instance internally coated hollow conductors. However, it is technically difficult to group together the radiation beam at a detector having sufficiently small dimensions.
In German Patent Publication No. 2,836,462 there is described a room or area monitoring receiving device wherein the infrared radiation is directed by a focusing lens through a tube onto a radiation transducer or converter arranged at the focal plane. By means of a reflection layer or coating arranged at the inner surface of the tube it is possible by accomplishing multiple reflections to project radiation emanating from further sector-shaped regions upon the radiation transducer. The sensitivity of the monitoring device is, however, markedly reduced for the outer regions because of the curved focusing surface of the focusing means.